I had a brief Twitter conversation with Anand Shimpi of Anandtech about this, and he was as perplexed as I was. Nobody could explain the technical basis for this vast difference in idle power management on the same hardware. None of the PC vendors he spoke to could justify it, or produce a Windows box that managed similar battery life to OS X. And that battery life gap is worse today - even when using Microsoft's own hardware, designed in Microsoft's labs, running Microsoft's latest operating system released this week. Microsoft can no longer hand wave this vast difference away based on vague references to "poorly optimized third party drivers".

The new Surface Pro 2 gets 6.6 hours of web browsing battery life. The MacBook Air 11", which has more or less the same hardware and battery, gets more than 11 hours.

I have a Surface RT - the first generation - and as such, I know why. Windows 8 might have Metro running on top of it hiding a lot of it, but Windows 8.x carries just as much baggage, cruft, and outdated shit with it as previous versions of Windows have. Windows 8/8.1 - and Metro in particular - simply suck. Slow, clunky, jarring, cumbersome, battery-sucking, restricted, and limited, with a crappy selection of rush-job, rarely updated applications. You know how resizing windows on Windows 7 or OS X is all nice and fluid? Why, then, is it a slow and jittery operation that brings Windows 8 Metro to its knees?

It's simple: just like battery life, it's a symptom of Microsoft's Windows team not having the balls to truly go for a clean break, as the Windows Phone team have done. And lo and behold, Windows Phone - even WP8, which runs on the same NT kernel - has none of the slowness and crappiness issues that continue to plague Windows 8 Metro (although WP has its own set of issues unrelated to these).

If you want a smooth, modern laptop today - get a MacBook. If you want a smooth and modern tablet, get the Nexus 7 or an iPad. Microsoft still has nothing to show for itself in these areas.

Windows is quite behind when it comes to powersaving. The features landing now (like tickless kernel) were available in Linux years ago. Runtime power management (turning off devices not being used at the moment) is almost nonexistant in Windows. Additionally, Linux is in special position - the same Linux (or very similar - with android addons) is used on mobile devices and on laptops. Almost every optimizations mobile companies implement for cellphones also works on laptops, bringing power usage down.

More exotic OSes, like Darwin/Mac OS X, outpace Windows when it comes to integration with the hardware. For example Apple, controlling both hardware and software, was able to quickly introduce "half wake/half suspended" state - google for "darkwake".

My knowledge is outdated, but with Windows 7 and Ubuntu, Windows 7 had longer batter life on same laptop. Anecdotally, Ubuntu running as a guest on Windows host had more battery life than running Ubuntu on hardware.

So this comes a little shocking (that and how someone compared Surface and MacBook Air, back in my days battery tests wre done on same hardware.

My knowledge is outdated, but with Windows 7 and Ubuntu, Windows 7 had longer batter life on same laptop.

One of the reasons for this could be the lack of power-management in GPU-drivers. You don't mention if you were testing with F/OSS-drivers or closed-source ones, or even what GPU you had, but AFAIK neither the F/OSS-drivers for NVIDIA-cards or for the AMD-cards properly support power-management.

OS that the producer cares about providing customers with backwards compatibility is slower to adopt new features than other Operating systems where they don't guarantee any backward compatibility or even care about it.

What a surprise!

Usually Windows gets better battery life, Linux with Jupitur Applet or similar brought them more or less in line. I get about 4 hours on my very old laptop.

6.6 hours of battery life on a single charge and people are complaining? I am used to 4 hours if the screen is dark as f--k and I don't fire up VS.